1. Field of the Invention
This invention relates to a novel photorecording element which utilizes a change in the orientation of liquid crystal by light and to a liquid crystal cell comprising the same photorecording element. More particularly, this invention relates to a photorecording element which effects temporary or permanent recording of information by utilizing the change caused in the orientation of a liquid crystal layer by a compound capable of reversibly changing structure upon irradiation by light and to a liquid crystal cell which comprises the photorecording element.
2. Prior Art Statement
As recording elements using a liquid crystal, those which depend on the storage of information by electrical action and those which depend on the storage of information by the action of light have been known to the art. Those of the former kind are chiefly used for display devices.
The liquid crystal display which writes information by virtue of an electrical action suffers erasure of information when the power supply is turned off and, therefore, requires a special device to ensure permanent preservation of information. Further, since it inevitably uses patterned electrodes, it has an insufficient resolving power and is not suitable as a recording element of high capacity.
The recording elements which effect storage of information by the action of light include those of the type which utilize the heat generated by a light of high luminance such as a laser beam which causes a change in the phase of liquid crystal and those of the type which effect a change in the phase of liquid crystal by the action of light caused through the agency of a compound having an ability to change structure photochemically and which is incorporated in the liquid crystal in advance
The recording elements of the type utilizing heat, such as of a laser beam, are usable for high-density recording. Since they can be used only for bit recording, however, they have only limited applications. Then, the recording elements of the type which attain a change in phase by virtue of the action of a light upon a compound able to change structure photochemically and incorporated in the liquid crystal in advance exhibit an outstanding resolving power during the early stage of the storage of input information. Because of the fluidity of liquid crystals, however, they are liable to suffer a remarkable loss of resolving power with lapses of time. For example, the photochromic cholesteric liquid crystal which is obtained by dissolving azobenzene, a chiral compound, in a nematic liquid crystal is transformed by the action of ultraviolet light into an isotropic phase and is enabled to attain recording of information by virtue of this transformation of phase. However, it has a disadvantage in that the liquid crystal eventually begins to flow and the recorded image begins to lose sharpness (Glossary of Lectures for the 52nd Spring Meeting of Japan Chemical Society, 1986).